Re: Using tn5250

Hi Holger,

Yes our next stage is to capture wireless packets.

You're right of course about the TCP, I'd left that out of my thinking
but shouldn't have done.  We do see that on the gateway captures.

Regards

Robin Wenham
Absolute Network Solutions Ltd



-----Original Message-----
From: linux5250-bounces-Zwy7GipZuJhWk0Htik3J/[email protected]
[mailto:linux5250-bounces-Zwy7GipZuJhWk0Htik3J/[email protected]] On Behalf Of Holger Schurig
Sent: 09 February 2010 11:13
To: linux5250-Zwy7GipZuJhWk0Htik3J/[email protected]
Cc: Marek Bajon
Subject: Re: [LINUX5250] Using tn5250

> When you press ENTER (or any function key), the data entered is
> sent to your server and then a response (display refresh) is
> sent back to the workstation from your server. If a packet is
> lost in either direction the communication is "out of sync" -
> the display waits for an answer from the server which is not
> coming because: 

That is only half-ways true. Telnet doesn't use UDP, it uses TCP. 
And here the TCP/IP-Stacks (on your box and on the AS/400) will 
automatically retry the "lost" packet when no explicit or 
implicit ACK comes back. On Linux, this retry-behavior is 
tuneable, e.g. via /proc/sys/net/ipv4. 


> answer was totally / partially lost in the network.

A totally lost answer will terminate the TCP/IP connection.

However, note that with the default settings this can take a 
looooong time (more than half-n-hour!), because of the 
exponential backup.


Just run wireshark / tshark on your client, press the ENTER key 
and observe the behavior. Now dismount the antenna on your AP 
and again press the ENTER key. And see what happens now :-)  Be 
sure to keep tshark running until the connection will be 
terminated. 



Best regards,
Holger

-- 
http://www.holgerschurig.de
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